On-chip Inductors and Transformer Applied Electronics Conference SP1.4 Supply on a Chip - PwrSoC Palm Springs, California 25 Feb 2010 James J. Wang Founder LLC 3131 E. Muirwood Drive Phoenix, Arizona 85048 James.Wang@Consultant.com APEC 2010 www.consultant.com 1
RFIC s Planar Spirals < 10 nh Eddy currents Not over actives EMI NEC Electronics APEC 2010 www.consultant.com 2
On-chip Inductors 5nH to 2700nH Low Rdc, 9 µm thick gold RF skin effect Magnetic cores >100 µm thick Optimize to frequencies Low cost production processes Flexible design, trim-able Minimize EMI directly over active IC circuits Small; multiple inductors onto existing chips APEC 2010 www.consultant.com 3
Linear Inductor wires < 250 µm loop height 54 µm wire pitch Electroplated gold line Form tiny gold coils APEC 2010 www.consultant.com 4
Over Passivation Metals 18 µm thick gold bumps 9 µm thick TAB for LCD Driver ICs Wire bond pad & interconnect line for microcontrollers Publication: for 175C Tj-max, J. Wang and B. Baird at Pan Pacific Microelectronics Symposium, Feb. 2003, pp241 APEC 2010 www.consultant.com 5
on IC Aluminum or copper layers underneath gold OPM interconnects APEC 2010 www.consultant.com 6
Wire Bonds onto Pads pads Wire bonds over actives Stronger gold-bold bonds 3x more gold in 2 mils wires than electroplated gold on-chip APEC 2010 www.consultant.com 7
Toroidal Inductor 700 µm diameter; measures 8 nh from 1-300 MHz Q = 7 APEC 2010 www.consultant.com 8
Advantages of Inductors TM Tiny: < 1 mm diameter x 0.25 mm height Fits 1 mm thin QFN packages Integrate 2, 4, 16 or more on-chip inductors Add onto existing ICs ball bonds + electroplated thick gold Production ready, low cost Volume processes & tools Lower cost than discretes (0402 chip-inductors) Alter inductance by adjusting wire loop height is ideal > GHz, RF frequencies APEC 2010 www.consultant.com 9
Inductor Physics L = µ 0 n 2 l A Area L = inductance value µ 0 4π x 10-10 Henry/mm n number of turns/unit length l length of inductor coils A cross-sectional area of linear inductor l APEC 2010 www.consultant.com 10
Larger Air Core Toroids Toroidal inductors; 1.0 mil Au wires; 10 mil loop height 2.5E-07 Inductance (Henry) 2.0E-07 1.5E-07 1.0E-07 Practical limit Too large 128 turns_1.0 mil 64 turns_1.0 mil 32 turns_1.0 mil 16 turns_1.0 mil 5.0E-08 0.0E+00 0.00 10.00 20.00 30.00 40.00 50.00 Circular Area (mm2) APEC 2010 www.consultant.com 11
Ferrite Core Inductor 1 mm 9 Turns 1x2x0.2 mm 150 nh Q = 6 @ 2.4 MHz APEC 2010 www.consultant.com 12
11 Turns Inductor 2 mm Ring oscillator, transistors test structures underneath inductor to evaluate interference. APEC 2010 www.consultant.com 13
Rdc & Inductances Ferrite Cores measured @ 5 MHz 2 ferrite materials Parallel wires L (n H ) 800 700 600 500 400 300 200 100 0 0 2 4 6 8 10 12 14 Number of Turns L or Rdc 500 450 400 350 300 250 200 150 100 50 0 0 5 10 15 Number of turns R (mohm; 2 wires) R (mohm; 3 wires) L (nh; 3 wires) L (nh; 2 wires) Measurements: Marilyn Stuckey & Hanyu Sheng APEC 2010 www.consultant.com 14
Magnetic Field Lines Ferrite core 35 turns coil designed to keep the EM field lines within the core, parallel to IC surface 2 mm >1500 nh APEC 2010 www.consultant.com 15
Isat > 1A Measured L @ 5MHz decreased less than 1%; tested to 1 A Ferrite core APEC 2010 www.consultant.com 16
Designing Transformer primary/secondary coils Insulator between two layers minimizes eddies 1 mm 35 turns; permalloy core 2.7 µh APEC 2010 www.consultant.com 17
Material Possibilities Inductor cores: Air (lowest cost) Ferrites (130 µm thick) High permeability permalloy (105 µm thick) Glob-top with magnetic filler particles Other materials not yet tried Round, rectangular, octagonal, etc. Custom for frequency, L, Q APEC 2010 www.consultant.com 18
Ready for IC Evaluations Layout inductors over existing ICs Design & processes available Prototype then evaluate Characterize & optimize ESD, spike current protection Shrink hand-held devices Lowers cost Publication: Flexible On-chip Inductors and Transformer, J. Wang, IMAPS Device Packaging Conf, Ft. McDowell, Arizona 10Mar10 APEC 2010 www.consultant.com 19